The present invention relates to windows used in appliances. More particularly, this invention relates to appliance windows which are coated with a thermochromic polymer dispersed liquid crystal material.
Many appliances in use today have a clear glass window for allowing consumers to see what is going on inside the appliance. Unfortunately, the transparent nature of the glass window also detracts from the aesthetics of the appliance because the window does not match the design of the rest of the appliance which is usually of a particular color.
Windowless appliances, while perhaps aesthetically pleasing, have the major disadvantage of requiring consumers to open the door of the appliance to see what is going on inside. This results in a loss of heat.
Thus, it is desirable to provide an appliance window which will allow consumers to see what is going on inside the appliance without requiring the consumer to open the appliance door and further without detracting from the overall appearance of the appliance.
The use of thermochromic materials in connection with appliances is known in the art. Reference is made, for example, to U.S. Pat. Nos.: 4,983,810 (Balderson); 6,037,572 (Coates, et al.); 5,451,932 (Wunderlich et al.); and 5,326,174 (Parker). However, none of these references teaches the use of a thermochromic coating on the appliance window.
U.S. Pat. No. 5,337,727 (Borens et al.) mentions the possibility of using in an appliance window thermochrome panes the radiation permeability of which decreases as the temperature increases. However, the Borens et al. patent then teaches away from the use of such panes because "this impairs the view through the window" (col. 1, lines 56-59). Thus, Borens et al. teaches away from using thermochrome materials in an appliance window if it is desired that the view through the window not be impaired.
In recent years, certain polymer-dispersed liquid crystal ("PDLC") materials have been used as thermochromic (also referred to as temperature-responsive) materials. These particular PDLC thermochromic materials represent an improvement over previously used thermochromic materials because the PDLC materials have greater thermal stability and provide better visual contrast between the opaque and the clear states.
U.S. Pat. Nos. 4,688,900 (Doane et al.) and 4,685,771 (West et al.) each teach the use of temperature-responsive PDLC materials for use in displays but not on windows, particularly windows for use in appliances. U.S. Pat. Nos. 4,890,902 (Doane et al.); 4,994,204 (Doane et al.); 5,240,636 (Doane et al.); and 5,004,323 (West) teach the use of PDLC materials for use on windows but these materials are activated by electrical or magnetic means (i.e., these materials are "electro-responsive" or "magneto-responsive" rather than temperature-responsive) and, further, the windows on which these materials are applied are not appliance windows.
The use of temperature-responsive materials, rather than electro-responsive or magneto-responsive materials, in an appliance window is desirable because the temperature-responsive materials will be activated by the thermal energy released by the appliance during operation thereof. In other words, instead of requiring the active application of an electrical or magnetic stimulus to the material, the temperature-responsive material will be activated passively by the appliance's release of thermal energy.
Thus, it would be desirable to provide an appliance window coated with a thermochromic PDLC material.
In accordance with the foregoing, a primary object of this invention is to provide an appliance window which allows a consumer to see what is going on inside an appliance without opening the appliance door and which does not detract from the overall appearance of the appliance.
A further object of this invention is to provide an appliance window which is coated with a thermochromic material that allows a consumer to see what is going on inside an appliance without opening the appliance door and which does not detract from the overall appearance of the appliance.
Another object of this invention is to provide the aforementioned coated appliance window wherein the thermochromic material is a polymer-dispersed liquid crystal material having good thermal stability and which is capable of providing a good visual contrast between the opaque and transparent states of the material.
A still further object of this invention is to provide an appliance having a window coated with the thermochromic material having the features described in the foregoing objects.
These and other objects are achieved in the present invention.